The present invention relates to an improvement in a surface treatment apparatus such as an etching apparatus or a deposition apparatus, and in particular it relates to a means for activating a material gas, which is suitable for improving the treatment speed (etching speed, deposition speed, etc.) and controlling the reactions relating to the surface treatment.
Current surface treatment apparatuses, such as plasma etching apparatuses or plasma deposition apparatuses, are required to improve the treatment speed and to control the reactions of the surface treatment. These demands are directly related to improvements in mass-producibility, reproducibility, and controllability.
FIGS. 1 and 2 illustrate schematic diagrams of plasma etching apparatuses. The apparatus in FIG. 1 uses the RF discharge (13.56 MHz), while the apparatus in FIG. 2 uses magneto microwave discharge.
In FIG. 1, parallel plate electrodes 12a and 12b facing each other are provided in a surface treatment chamber 11. A material gas is introduced into the surface treatment chamber 11 through a valve 13, and then RF discharge occurs between the electrodes 12a and 12b.
In FIG. 2, microwaves generated by a magnetron 22 are led into a quartz discharge tube 25, through a waveguide 23. A magnetic field is formed by a coil 26 within the discharge tube 25. The interior of the waveguide 23 is kept at atmospheric pressure, while the interior of the discharge tube 25 and the surface treatment chamber 21 is evacuated so that they are in a vacuum. The material gas which will be subjected to the discharge is supplied through a valve 24 into the discharge tube 25, wherein a microwave discharge is generated. The microwaves are absorbed efficiently by the plasma by adjusting the magnetic flux density, so that a stable high-density plasma is obtained. A specimen 28 placed on a turn table 27 in the surface treatment chamber 21 is subjected to treatment such as etching by reactive species generated by the microwave discharge.
According to most of the methods of introducing the material gas into the surface treatment chamber in these apparatuses, the material gas is introduced, as it is, into the surface treatment chamber 11 or 21, or the discharge tube 25. A similar method is also used in a plasma deposition apparatus. When the ionization rate .UPSILON. in these apparatuses is defined as
.UPSILON.=n.sub.p /(n.sub.p +n.sub.o) PA1 n.sub.p : plasma density PA1 n.sub.o : density of material gas,
the value of .UPSILON. is a few percent even in the magneto microwave plasma etching apparatus shown in FIG. 2 in which the ionization efficiency is high (K. Sujuki et al., Jpn. J. Appl. Phys. 16, 1979 (1977)). The value of .UPSILON. is even smaller for the parallel plate plasma etching apparatus using RF discharge shown in FIG. 1. In addition to reactive ions, there are various neutral active species in a plasma. However, most of the material gas particles are not dissociated. In order to improve the speed of treatment, it is necessary to dissociate the particles of material gas efficiently and ionize them.
To provide an efficient dissociation and further ionization of the particles of the material gas, it has been proposed to excite the particles of the material gas preliminarily by RF discharges in a preceding stage from which the particles are sent to the discharge tube or the surface treatment chamber. A concrete example of this preliminary excitation is shown in FIG. 3. As shown in the figure, a preliminary treatment chamber 33 is provided as the stage before a surface treatment chamber 31 within which parallel plate electrodes 32a and 32b are provided with a specimen 38 placed on the electrode 32b. A pair of parallel plate electrodes 35a and 35b are provided in the preliminary treatment chamber 33, whereby RF discharge is generated. With such a construction, part of the gas introduced into the preliminary treatment chamber 33 through a valve 34 is excited and dissociated to promote the dissociation and ionization of the particles of gas in the surface treatment chamber.
As described above, the preliminary excitation by RF discharge has an effect on the improvement in the speed of treatment. This method is accompanied, however, by the difficulty in controlling the reaction. The electrons in a discharge usually have a wide range of kinetic energy, so that almost all the bonds between the atoms consisting of particles of the material gas are broken by the RF discharge. Accordingly, it is impossible to generate specific species and send only those specific reactive species into the surface treatment chamber. Since many different kinds of reactive species are sent into the surface treatment chamber and subjected to further discharge, very many kinds of reactive species are generated in the surface treatment chamber. As a result, the chemical reactions become very complicated when surface treatment is performed, the controllability of the reactions is reduced, and the reproducibility of the surface treatment is also reduced.
Therefore, preliminary excitation by using RF discharge has a disadvantage that it is accompanied by a difficulty in controlling the surface reactions, although it improves the speed of treatment.